Praise be to Allaah.

Firstly: 

The fast for which Allah forgives the sins of two years is fasting the day of ‘Arafah. As for fasting ‘Ashoora’, Allah forgives for that the sins of one year. 

For the virtues of fasting the day of ‘Arafah, please see the answer to question no. 98334; for the virtues of fasting on the day of ‘Ashoora’, please see the answer to question no. 21775. 

Secondly: 

There is no doubt that drinking alcohol is a major sin, especially if one persists in doing so. Alcohol is the mother of all evils. The Prophet (blessings and peace of Allah be upon him) cursed ten people with regard to alcohol. At-Tirmidhi (1295) narrated that Anas ibn Maalik (may Allah be pleased with him) said: The Messenger of Allah (blessings and peace of Allah be upon him) cursed ten with regard to alcohol: the one who squeezes (the grapes etc), the one for whom it is squeezed, the one who drinks it, the one who carries it, the one to whom it is carried, the one who pours it, the one who sells it and consumes its price, the one who buys it and the one for whom it is bought.

Classed as saheeh by al-Albaani in Saheeh at-Tirmidhi 

What you have to do is give it up and repent from drinking it, and turn to Allah. 

Fasting on the day of ‘Ashoora’ or ‘Arafah only expiates minor sins; as for major sins, they require sincere repentance. 

Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said:

It is narrated in saheeh reports from the Prophet (blessings and peace of Allah be upon him) that fasting the day of ‘Arafah expiates (the sins of) two years and fasting the day of ‘Ashoora’ expiates (the sins of) one year. But saying that it expiates does not mean that major sins can be expiated without repentance. The Prophet (blessings and peace of Allah be upon him) said that from one Jumu‘ah to the next and from one Ramadan to the next “expiate what comes between them so long as one avoids major sins.” It is well known that prayer is better than fasting, and fasting Ramadan is better than fasting the day of ‘Arafah, and fasting on these occasions does not expiate bad deeds unless one avoids major sins, as stipulated by the Prophet (blessings and peace of Allah be upon him). So how can anyone think that observing a voluntary fast of one or two days will expiate for zina, stealing, drinking alcohol, gambling, witchcraft and the like? 

This cannot be the case. 

End quote from Mukhtasar al-Fataawa al-Masriyyah, 1/254. 

Ibn al-Qayyim (may Allah have mercy on him) said: 

One of them said that the day of ‘Ashoora’ expiates for the sins of the entire year and fasting ‘Arafah adds to the reward. This deluded person does not realise that fasting Ramadan and offering the five daily prayers is greater and better than fasting the day of ‘Arafah and the day of ‘Ashoora’, and they only expiate for the time between them if major sins are avoided. 

From one Ramadan to the next, from one Jumu‘ah to the next, is not enough to expiate minor sins unless that is accompanied by avoidance of major sins, then the two things referred to will be able to expiate minor sins. 

How can observing a voluntary fast for one day expiate for all major sins a person commits and persists in, when he does not repent from them? That is impossible. 

However there is nothing to suggest that fasting the day of ‘Arafah and the day of ‘Ashoora’ cannot expiate for all the sins of the year in general; in that case the hadeeth should be interpreted as one of the texts that promise reward provided that the conditions are met and the impediments avoided, and persisting in major sins is an impediment to expiation. So if one does not persist in major sin, fasting and not persisting (in sin) together will be able to achieve expiation in a general sense, just as Ramadan and the five daily prayers, along with avoidance of major sins, are able together to bring about expiation of minor sins, even though (only one condition is mentioned in the verse in which) Allah, may He be glorified, says (interpretation of the meaning):

“If you avoid the great sins which you are forbidden to do, We shall remit from you your (small) sins, and admit you to a Noble Entrance (i.e. Paradise)”

[an-Nisa’ 4:31].

Thus we learn that the fact that one thing is made a cause for expiation does not rule out the fact that it could be supported by another cause; expiation when two causes are combined is more likely and better than that for which there is only one cause. The stronger the means of expiation, the more likely it is and the more perfect and comprehensive it will be.

End quote from al-Jawaab al-Kaafi, p. 13 

At-Tirmidhi (1862) narrated that ‘Abdullah ibn ‘Umar said: The Messenger of Allah (blessings and peace of Allah be upon him) said: “Whoever drinks alcohol, Allah will not accept any prayer from him for forty days, but if he repents, Allah will accept his repentance. Then if he goes back to it, Allah will not accept any prayer from him for forty days, but if he repents, Allah will accept his repentance. Then if he goes back to it, Allah will not accept any prayer from him for forty days, but if he repents, Allah will accept his repentance. Then if he goes back to it a fourth time, Allah will not accept any prayer from him for forty days, but if he repents, Allah will not accept his repentance and He will cause him to drink from the river of al-Khabaal.”

Classed as saheeh by al-Albaani in Saheeh at-Tirmidhi. 

Al-Mubaarakfoori said in Tuhfat al-Ahwadhi: It was said that prayer is singled out for mention because it is the best physical act of worship; if it is not accepted, then it more likely that other acts of worship will not be accepted either.

End quote from Tuhfat al-Ahwadhi, 5/488. This was also the view of al-‘Iraqi and al-Mannaawi 

See also the answer to question no. 38145 

If acts of worship are not accepted when one persists in drinking alcohol, then how can the fast of ‘Ashoora’ be accepted? Indeed, how can it expiate for the sins of a year? 

What you have to do is hasten to repent sincerely and give up what you are doing of drinking alcohol, make up for what you have neglected and do a lot of the good deeds that will abide, in the hope that Allah will accept your repentance and forgive you for what you have done in the past of being heedless and transgressing the limits set by Allah. 

Thirdly: 

What we have said to you here does not mean that you should not fast on ‘Arafah or ‘Ashoora’, or not do any other naafil good deeds such as praying, fasting, giving charity or offering sacrifices. Drinking alcohol does not mean that you cannot do any of these things. Falling into major sin does not mean that you should refrain from doing acts of worship and good deeds; that would only make the matter worse. Rather you should hasten to repent and give up (that sin), and do a lot of good deeds, even if your nafs gets the better of you and you fall into some sins. But the validity of the deed and its acceptance are one thing, and the particular virtue of expiation for the sins of one or two years is something else. Ja‘far ibn Yoonus said: I was in a caravan in Syria, when some Bedouin came out and seized it, and they started showing it to their leader. They brought out a sack in which there was sugar and almonds, and they ate from it but the leader did not. 

I said to him: Why are you not eating? He said: I am fasting! 

I said: You attack travellers and take wealth and kill people, but you are fasting?! 

He said: O shaykh, I am maintaining some connection with Allah so that one day I may repent. 

After a while, I saw him circumambulating the Ka‘bah, and he was in ihram. I said: Are you that man? He said: That fast brought me to this place! 

(Tareekh Dimashq, 66/52) 

See also the answer to question no. 14289.